Secondary batteries, which are easy to apply to various product groups and have electrical characteristics such as high electrical energy density, are used not only for portable devices but also for electric vehicles (EV), hybrid electric vehicles (HEV), energy storage devices or the like, which are driven by electric power sources. The secondary batteries are attracting attention as a new energy source for enhancing eco-friendliness and energy efficiency since they have a primary advantage of dramatically reducing the use of fossil fuels and also no by-products are generated by the use of energy.
A battery pack applied to the electric vehicle or the like has a structure in which a plurality of battery modules, each having a plurality of unit cells, are connected in series and/or in parallel to obtain high output. Also, the unit cell includes positive and negative electrode current collectors, a separator, an active material, an electrolyte solution and the like to be repeatedly charged and discharged by electrochemical reaction among these components.
Meanwhile, since a middle-sized or large-sized battery pack is manufactured such that a plurality of battery modules are densely arranged in a narrow space, it is very important to emit heat generated from each battery cell.
Since the secondary battery is charged or discharged by the electrochemical reaction as described above, the battery is affected by the ambient temperature condition environment. For example, if the secondary battery is charged or discharged in an extremely poor temperature condition such as at a cryogenic or hyperthemic temperature, the charging and discharging efficiency of the battery is lowered, and thus it may be difficult to ensure the normal operation performance. In particular, since a lithium ion secondary battery may ignite or explode when exposed to a high temperature environment for a long time, the related industry is focusing on the development of a middle-sized or large-sized battery pack having a high output capacity and excellent cooling efficiency.
As a method of emitting heat generated from the battery module, Korean Unexamined Patent Publication No. 10-2014-0077272 discloses a method of cooling battery modules using a heatsink in which a coolant flows.
Meanwhile, as shown in FIG. 1, in order to cool a battery module 1 using a heatsink, a thermal interface material (TIM) 3 is interposed between the battery module 1 and the heatsink 2. The TIM 3 functions to reduce the thermal contact resistance between the battery module 1 and the heatsink 2 by filling void spaces created due to the surface roughness of the contact surfaces thereof. Currently, a thermal pad or resin with high thermal conductivity is widely used as the TIM 3.
However, the resin-type TIM has a problem in product application and quality control, and the thermal pad-type TIM has significantly lower cooling efficiency, compared to the resin-type TIM, though it is advantageous in product application and quality control.
Thus, there is demanded a new battery pack cooling method which may improve the cooling efficiency by effectively reducing the thermal contact resistance between the battery module 1 and the heatsink 2, while ensuring easy process and quality control.